Which software to use for a newsletter

Having had my practice going a few months now I have collected enough email addresses to make a newsletter worthwhile (also as a why of keeping in touch with slow burning prospects).

I have a couple of questions. Firstly, what software do people use to a) create the newsletter and b) mail it. I've heard good things about Mailchimp, but know little about it. I also have a copy of Sage ACT (installing that and getting my head round it are next on my to do list).

Also, does anyone have any thoughts on incorporating the newsletter into my website and mailing links to by mailing list (and so I can also distribute the link via Twitter)

Final question - any thoughts on content for the newsletter would be welcome. My thoughts so far:

General business/tax news

Practice news (new clients, client success stories, etc)

Tax Tip of the month

Profit improvement tip of the month

Client interview (a handful of standard interview type questions for each client to answer - will promote them, (hopefully) they say nice things about me, and it's one less thing I need to write)